1. Field of the Invention
The invention relates to integrated optical lightguide devices and more particularly to optical waveguide sensors, modulators and spectrophotometers.
2. Description of the Related Art
Integrated optical sensors are known from an article entitled “Fabrication and Packaging of Integrated Chemico-Optical Sensors” by R. G. Heideman et al., published in Sensors and Actuators, volume B 35–36, 1996, pp. 234–240. Besides sensors and actuators in a general sense, the article describes in particular a Mach-Zehnder interferometer including a deposited film, which is sensitive to air humidity. The article furthermore describes an embodiment wherein an optical fiber for light supply is integrated in the Mach-Zehnder sensor.
Generally, such a device is much too complicated for practical applications and also relatively costly, and in some cases it is sensitive to interfering parameters or to small deviations between intended and realised local refractive index profiles.
The operation of known integrated optical sensors and actuators, such as the Mach-Zehnder interferometer, is usually based on a phase change of the light being used, induced by a controlling parameter (actuator) or a parameter to be measured (sensor). This imposes restrictions as to the type of light sources to be used. For the lightguide structures to be used this means that transitions to and from elements in the optical structure will have to be provided very gradually in the direction of light propagation, resulting in relatively long structures.
U.S. Pat. No. 4,913,519 (corresponding to WO 8908273) also discloses an optical sensor structure wherein an optical fiber is covered with a periodic, interrupted cladding layer in such a manner that a parameter to be detected, a change from water to ice and from ice to water, causes the sensor operation to switch between an “off” condition where there is no light transmission when water is present and an “on” condition where light is transmitted when the water changes to ice. This patent illustrates the use of segments of identical length which are periodically spaced, but is otherwise very limited in application.